Higher integration of semiconductor devices is desired for, e.g., superior performance and/or reducing the price of electronic devices. In the case of semiconductor memory devices, integration may be an important factor in determining product price. The integration level of typical two-dimensional or planar semiconductor memory devices may be determined, e.g., by the area occupied by a unit memory cell. Accordingly, in such devices, integration may be influenced by the level of fine pattern forming technology used in a manufacturing process. However, the processing equipment needed to increase the fineness of patterns may be expensive and may set a practical limitation on increasing integration for two-dimensional or planar semiconductor devices. Accordingly, three-dimensional semiconductor memory devices having three-dimensionally arranged memory cells have been proposed.